In the past, CBN abrasive belts and grinding wheels have been very difficult to true. This is because the CBN grains on the belt or wheel are extremely hard, and somewhat slippery, that is, they can be fairly easily dislodged from their bond. Because of their hardness (slightly less than diamond), a great deal of force is required to cut the CBN grains with a diamond trueing wheel. Because the CBN grains are somewhat slippery, it is difficult for the bond to retain them.
A typical diamond trueing wheel employs diamonds that are anywhere from 0.7 millimeters (mm) to 2.0 mm in diameter, and when the trueing wheel is new, the contact area is relatively small. As the trueing wheel wears down, the contact area becomes larger and larger, because the diamond particles are worn down to their maximum cross-dimension. The trueing force increases as the contact area increases and accordingly long before the diamond is worn out, the CBN grains start to dislodge from the bond.
As the diamonds on the trueing wheel wear, additional adjacent diamonds come in contact with the belt or wheel being trued and this also substantially increases the contact area, with the result that the trueing force increases and the quality of trueing goes down. This decrease in quality begins even before the CBN grains begin to dislodge from the bond.
It has been found that it is of great importance to reduce the amount of force on the CBN grains during trueing, so that they do not come loose or dislodge. It is also important to maintain the force of contact uniform and constant throughout the life of the trueing wheel, preventing any substantial increase in this force, so that the quality of trueing is consistent.
One way of accomplishing this, in accordance with the invention, is by reducing the size of the diamond particles used in the trueing wheel to about 0.150 mm diameter. This assures that the contact area will remain small and the CBN grains will not be dislodged.
Further, in accordance with the invention, the radially outer surface of the trueing wheel is formed at an acute angle to its axis of rotation, rather than perpendicular to the axis of rotation as has been done in the past, and only a single layer of the diamond particles is applied to the outer surface. As the trueing wheel wears down, there are new, small diamond particles exposed so that the trueing wheel performs virtually the same as when it was new, without any appreciable increase in the amount of force applied.
One object of this invention is to provide a trueing wheel having the foregoing features.
Another object is to provide a trueing wheel of relatively simple, inexpensive construction, which is durable and long lasting, and which can be relatively inexpensively manufactured.
Other objects, features and advantages of the invention will become more apparent as the following description proceeds, especially when considered with the accompanying drawings.